Atypical giant parathyroid adenoma is a rare tumor with unusual histological features, an unusual presentation of primary hyperparathyroidism but more elevated laboratory findings and more severe clinical presentation due to larger tissue mass, and defined as weighing>3.5 g, leading to diagnostic and therapeutic challenges. Herein, we report a case of a 56-year-old woman who presented with a palpable neck mass, fatigue, persistent hypercalcemia, osteoporosis and asymptomatic renal stones, Ultrasound showed a left-sided solid nodule, and Sestamibi nuclear scan showed a giant parathyroid adenoma. The diagnosis of giant atypical parathyroid adenoma was confirmed after surgical excision size (3.5*1.5cm). We discuss the investigations, treatment, and outcome of this rare case and highlight the importance of long-term follow-up care.